Decomposition of nitroparaffins in jet propulsion motor operation



tates Patent l'fritz Zwiciry, Pasadena, and Frederick J. Ewing,Attadena, Caiii, assignors to Aerojet Engineering Corporation, Azusa,Califl, a corporation of Delaware Uriginal application Mar. 31, 1944-,Ser. No. $28,893:,now Eatent No. 33483997, dated Aug. '7, i962. Bividedand this application Nov. 21, 1961, Ser. No. 163,945

Claims. (Cl- 60-354) the copending application of Zwicky et a1, SerialNo.

526,064, filed March 11, 1944, and now U.S. Patent No. 2,433,943, issuedJanuary 6, 1948, as a liquid fuel containing its own oxidizer.Decomposition of such a fuel may be accomplished by a catalyst withinthe motor, for example, a surface prepared from metal oxides.

Such catalytic surfaces, usually in the form of liners, sometimes tendto be brittle or friable and may require frequent replacement. Accordingto our invention a catalyst may be added continuously to the motorduring operation, thus insuring the constant presence of a sufiicientamount of catalyst to cause satisfactory auto-combustion of fuel.

'Our invention may be carried out by injecting the catalyst into themotor in the form of a colloidal suspension in a fuel. For example, thefinely divided catalyst may be mixed with ethyl alcohol or some similarnon-detonating fuel, and injected into the motor through a small slushinjector so as to intersect a spray of the fuel which is being injectedinto the motor.

An alternative way of carrying out the invention is to inject thecatalyst into the motor in the form of a fluid or of a solution whichwill break down in the combustion chamber to give one or more catalyticsubstances.

The invention will be better understood from the following detaileddescription and the accompanying drawing in which:

FIG. 1 shows a jet thrust motor in cross section along its longitudinalaxis;

FIG. 2 is an enlarged part view in cross section of the injector end ofthe motor shown in FIG. 1; and

FIG. 3 is a part view in cross section of a motor having another type ofinjector.

Similar numerals refer to similar parts throughout the several views.

In FIG. 1 we show a jet motor which consists of a tubular combustionchamber 1 suitably threaded on both ends, having in its right hand endan exhaust nozzle 2 threadedly secured, which contains an opening 3converging to a constricted portion 4 and diverging outwardly forming anexhaust opening 5. Near the opposite end of member 1 a spark plug 6 isinserted into its wall. In the opposite end of member 1 a plug-shapedmember 7 is threadedly secured. Member 7 contains in its center portionan injector plug 8 secured by lock nut 11. The plug 8 has a flared tubeconnection 56 in its outside end and a concentric hole 9 terminating inan injection nozzle 1i). Injector plug 8 is made leakproo'f by aninserted O ring 12. There is provided an annular groove 13. Beginning atgroove 13 a helical groove 14 is provided around the injector plug andthis helical groove terminates in a frusto conical end 15. End 15 ismachined to form an annular frusto conical space 16 in the recess 17 ofthe member 7. Recess 17 has a concentric orifice '18 which permits aspray of fluid from concentric hole 9 flared tube connection '25 isscrewed into member '7 in which another blind hole 26 is provided. Asmaller angular orifice 27 passes through member 7 from the end oforifice 26. Orifice 27 is so positioned that a fluid stream issuing fromit intercepts the stream from injector 3.

In operation the liquid fuel, such as nitromethane or a mixture ofnitromethane and nitroethane, is injected into the combustion chamber 1through tube 30, hole 9 and nozzle 16 of the injector plug 8.Simultaneously, a colloidal suspension of catalyst in a non-detonatingfuel is injected, through tube 31, flared tube connection Zih holes 21and 2-2 into groove 13 of injector plug 8 and through helix l4 andfrusto conical space 16 into the combustion chamber 1. Catalysts whichmay be conveniently used comprise iron oxide, chromium oxide, chromiumhydroxide, cerium oxide, or mixtures thereof, or other metal oxidescolloidally suspended in the nondetonating fuel which may, for example,be an alcohol. It is understood that this invention is not limited tothe compounds listed above, but may be also used with other metal oxidescatalytically active in the decomposition of suitable self-combustiblefuels.

During initiation of operation, oxygen or some other suitable oxidizingagent is injected through tube 32, flared tube connection 25, hole 26and angular orifice 27 impinging upon the spray of nitromethane and thecolloidal suspension of catalyst in a non-detonating fuel respectivelyas described above. The combined stream or spray is ignited by sparkplug 6. After the motor reaches a temperature sufiicient to permitcontinuous catalytic decomposition of the nitromethane or mixture ofnitromethane and nitroethane, injection of the oxidizer may bediscontinued.

When suitable precautions are taken to guard against overheating of theself-combustible fuel, the catalyst may be mixed with this fuel justbefore injection or may even be stored as a colloidal suspension in thisfuel. When this is done care must be taken to guard against explosion.

FIG. 3 is a cutaway view of a jet motor showing the injector end. Suchan injector may be used instead of the plug 7 of FIG. 2. With this thereis utilized a catalyst in the form of a fluid which is in itselfcatalytic or which will breakdown in the motor to provide one or moretypes of catalytic materials. This avoids the use of a suspension of asolid material and of an injector thereof, and consequently there is nodanger of a buildup of solid particles in the orifices and injector withconsequent stoppage of the motor. Instead the catalyst 18 injected intothe motor as a clear fluid.

In FIG. 3, part of cylindrical jet motor 1 is shown containing a sparkplug 6 in its upper portion and in its lower portion an injector 30consisting of a pipe plug 32 having a flare tube connection 31 at itsouter end. A nozzle 33 is provided in the wall of the motor 1 in linewith the injector Stl. This injector is set in such a way that anystream injected therethrough meets a counterstream injected through aninjector 25 through plugshaped member 34. Injector plug 35 screws intomember 34 and is locked with nut 45, and has a flared tube connection inits outside end. A concentric hole 36 passes through plug 35 andterminates in a hole 37 which is drilled normal to hole 36 in thecylindrical end of the injector. A groove 33 is machined around thesurface of member 35 concentric with hole 37. A helical groove 39 aroundmember 35 extends from groove 37 and terminates at the frusto conicalcap 40. Cap 40 and the conical recess 41 and orifice 43 contained inmember 34 form a frusto conical space 42 through which a singlepropellant may be injected into the combustion chamber 1.

In operation the nitroparaflin fuel is injected into the motor throughtube 46, injector plug 35, and hole 43. Simultaneously through injector30 and nozzle 33 a fluid is injected in opposition to the stream ofnitroparaflin fuel, which will act as a catalyst either of itself orafter reaction in the motor. The advantage of injecting the catalystfluid through in an opposite direction to the main propellant stream isobvious, since breakdown of such catalyst fluid is necessary to obtainmaximum catalytic activity. Such breakdown is brought about by thepickup of heat for evaporation and decomposition of the catalyst.

Initiation of combustion may be accomplished by the injection of oxygenor any other suitable oxidizing agent through tube 47, injector plug 25,hole 26, and angular orifice 27 impinging upon the stream ofnitroparafiin fuel and the stream of the catalyst. The combined streamsare ignited by spark plug 6.

Fluids suitable for catalysts may be liquid compounds, liquid solutions,gaseous compounds or gaseous mixtures. For example, liquid compounds maycomprise CrO C1 M11207, or Fe(CO) Liquid solutions will includesolutions of Ce(NO in methanol or Ca(MnO in water. Suitable gases mayinclude Ni(CO) vapor or a mixture of Ni(CO) vapor with oxygen. All ofthese are fluids and may be easily broken down in the combustion chamberto give products which are catalytically active in the decomposition ofsuitable self-combustible fuels.

As an example of such a catalyst and of its behavior when injected intoan operating jet thrust motor, consider the salt Ce(NO dissolved inmethyl alcohol. The ordinary commercial form of Ce (N09 containing someWater of hydration, may be liquefied by methyl alcohol in the ratio of 5grams of the salt to one cubic centimeter of alcohol. The viscosity maybe further reduced, if desired, by the addition of more solvent.

This solution may be continuously injected into the motor at a ratenormally only a few percent of that of the propellant. The injection isbest made in the form of a fine spray in order to obtain maximumcatalyst surface.

The first thing that occurs in the motor is the evaporation of thespray, yielding water vapor, methyl alcohol vapor, and Ce(NO in the formof fine particles. The

water vapor cools the motor slightly without substantial effect onperformance, and the methyl alcohol vapor burns and serves to someextent as additional fuel.

The Ce(NO decomposes according to the equation:

The CeO is a very active solid catalyst for the decomposition ofnitroparaffins, acting by heterogeneous catalysis, while both the O andthe N0 increase the rate of decomposition and flame speed ofnitroparaflins, acting by homogeneous catalysis. Furthermore, the O andN0 help make up an oxygen deficiency in the nitroparaflins, thusincreasing the available enthalpy and specific impulse. The solid CeOparticles will in part be ejected through the nozzle and in part adhereto the wall of'the motor, where their catalytic activity will becontinued.

In the use of the fluid catalysts, as in the case of the catalystsuspension, the fluid catalyst may be injected separately or in solutionin the self-combustible propellant. If used in the combustiblepropellant suitable precautions must be taken to prevent overheating ofthe catalystcontaining propellant, in order to avoid explosion.

In some instances it may be desirable to continue the injection of asmall stream of oxygen into the combustion chamber in order to obtainhigher specific impulses and higher velocities. In such instances it isadvantageous to continue the injection of the catalyst along with thesmall stream of oxygen as more rapid and complete combustion of theself-combustible fuel is thereby obtained.

This application is a division of our copcnding Serial No. 528,893 filedMarch 31, 1944, now U.S. Patent No. 3,048,007.

We claim:

1. The method of operating a jet motor utilizing a self-combustible fuelselected from the nitroparaflins, which comprises continuously injectinginto the combustion chamber of the motor during operation a fluid whichwill provide catalyst for the decomposition of the nitroparaflins, saidfluid being selected from the group consisting of CrO Cl Mn O Fe(CO)solutions of Ce(NO in methanol and Ca(MnO in water, and Ni(CO) vapor,said nitroparaflins being selected from the group consisting ofnitromethane and mixtures of nitromethane and nitroethane, and ignitingthe said nitroparaflins in the chamber thereby producing gases underpressure which are ejected out the exhaust nozzle.

2. The method of operating a jet motor utilizing a selfcombustible fuelselected from the nitroparaflins, the method which comprisescontinuously injecting into the combustion chamber of the motor duringoperation nitroparaflins containing a fluid which on heating willprovide catalyst for the decomposition of the nitroparatlins said fluidbeing selected from the group consisting of CrO Cl Mn O Fe(CO) solutionsof Ce(NO in methanol and Ca(.MnO in water, and Ni(CO) vapor and saidnitroparaflin being selected from the group consisting of nitromethaneand mixtures of nitromethane and nitroethane, and igniting the saidnitroparaifins in the chamber thereby producing gases under pressurewhich are ejected out the exhaust nozzle.

3. The method of operating a jet motor having a combustion chamber andan exhaust nozzle from the chamber which comprises injecting into thecombustion chamber nitromethane and a catalyst selected from the groupconsisting of CrO Cl Mn O Fe(CO) solutions of Ce(NO in methanol andCa(MnO in water, and Ni(CO) vapor and igniting the nitromethane in thechamber, thereby producing gases under pressure which are ejected outthe exhaust nozzle.

4. The process of decomposing nitromethane which comprises heating thenitromethane in the presence of a catalyst selected from the groupconsisting of CrO Cl M11207, Fe(CO) solutions of Ce(NO in methanol andCa(MnO in water, and Ni(CO) vapor.

5. The method of operating a jet motor having a com- 6 comprises heatingthe nitroparafiin selected from the group consisting of nitromethane andmixtures of nitromethane and nitroethane in the presence of a catalystselected from the group consisting of CIO CI Mn O Fe(CO) solutions ofCe(N0 in methanol and Ca(MnO in Water, and Ni(CO) vapor.

References Cited in the file of this patent UNITED STATES PATENTSStosick Jan. 6, 1948 2,433,943 Zwicky et a1. Jan. 6, 1948

1. THE METHOD OF OPERATING A JET MOTOR UTILIZING A SELF-COMBUSTIBLE FUELSELECTED FROM THE NITROPARAFFINS, WHICH COMPRISES CONTINUOUSLY INJECTINGINTO THE COMBUSTION CHAMBER OF THE MOTOR DURING OPERATION A FLUID WHICHWILL PROVIDE CATALYST FOR THE DECOMPOSITION OF THE NITROPARAFFINS, SAIDFLUID BEING SELECTED FROM THE GROUP CONSISTING OF CRO2CL2, MN2O7,FE(CO)5, SOLUTIONS OF CE(NO3)4 IN METHANOL AND CA(MNO4)2 IN WATER, ANDNI(CO)4 VAPOR, SAID NITROPARAFFINS BEING SELECTED FROM THE GROUPCONSISTING OF NITROMETHANE AND MIXTURES OF NITROMETHANE AND NITROETHANE,AND IGNITING THE SAID NITROPARAFFINS IN THE CHAMBER THEREBY PRODUCINGGASES UNDER PRESSURE WHICH ARE EJECTED OUT THE EXHAUST NOZZLE.